NEW YORK — John Green fans, mark your calendar.The author of the million-selling The Fault in Our Stars has a new novel coming Oct. 10, Dutton Books announced Thursday. The book is called Turtles All the Way Down and tells of a 16-year girl in search of a missing billionaire as she struggles with mental illness. Turtles is Green's first book since Fault in Our Stars, which came out in 2012.

In a statement issued through Dutton, Green said the new novel was both invented and personal in its taking on the theme of mental illness. Green's other books include Paper Towns and Looking for Alaska.